Atherosclerosis, the underlying cause of most human heart disease, results from a focal imbalance of the normal equilibria of the arterial wall. While metabolic cooperation between vascular cells is essential for the maintenance of normal vascular homeostasis, little is known about the nature of these interactions or whether disturbance of their equilibria will precipitate irreversible pathological changes in arterial tissue. We propose to investigate mechanisms of cellular interactions between vascular endothelium, smooth muscle cells (SMC) and monocyte-derived macrophages in vitro and in intact vascular tissue. Two separate general mechanisms of cell cooperativity will be studied: a) cell contact-mediated communication via gap junctional channels connecting the cytoplasm of adjacent cells, and b) humoral communication in which diffusible substances secreted by one cell type pass via the interstitial fluid to specific receptors on the surface of the other cell population. The effects of cell biological pertubations associated with hypercholesterolemia (cellular cholesterol, lipoprotein metabolism), a major risk factor for atherogenesis, will be investigated. New techniques to probe cellular communication in intact normal and atherosclerotic (fibrofatty lesion) vascular tissue will be tested and developed to integrate the in vitro findings with vessel wall biology and pathology. Gap junctional-mediated cell interactions will be investigated biochemically in vitro (transfer of 3H-nucleotides, fluorescent dyes and putative second messengers such as cyclic nucleotides and Ca++ and electrophysiological measurements) using cocultures of endothelial cells, SMC and macrophages. The effects of various mediators of gap junctional transfer, particularly cellular cholesterol composition, will be evaluated. The effects of heterocellular communication upon receptor-mediated lipoprotein metabolism in endothelial cells will be measured. Gap junctional communication will also be investigated in normal and atherosclerotic intact arterial tissues both at the ultrastructural level and functionally using new methods to deliver tracers to the vascular tissue. The regulation of platelet-derived growth factor-like mitogens (c-sis related) synthesized and secreted by endothelial cells will be investigated in the context of the interactions of these cells with SMC and macrophages using molecular biology techniques.